The invention relates generally to energy storage devices and systems, and more particularly to sodium-sulfur and sodium-metal-halide electrical energy storage devices and systems that exhibit an operational life and power density suitable for use in providing cost-effective and reliable electric energy storage solutions for electrical power grid renewable firming applications.
The greatest potential for significantly reducing green house gas emissions and reducing the US's petroleum consumption lies with the development and growth of renewable energy sources, such as wind and solar. To be optimally effective, a high penetration of these renewable energy sources into the electrical grid is necessary, as well as widespread electrification of the transportation systems. For either of these to occur, cost-effective and reliable electric energy storage solutions capable of delivering a wide range of power capabilities are needed.
When intermittent renewable power sources are connected to the grid, other power sources on the grid need to modulate their output in order to make up for the intermittency and ensure stable power output. The modulation service provided by these other sources is referred to as frequency regulation or renewable firming. At present, renewable firming is accomplished through the adjustment of output from excess conventional coal or gas power-generating units. However, as the renewable reaction of the grid power increases, an alternative non-green house gas emitting solution is desired. In particular, a cost-effective energy storage technology is required that can produce and absorb energy at the minutes to hours time scale and is scalable to the tens of megawatts power scale.
Desirably, a new energy storage technology would be provided that exhibits acceptable operational life so that the energy storage technology is suitable for use in renewable firming applications. The new energy storage technology will desirably provide a power density capability to provide an acceptable installed power cost. Any such technology will also desirably be capable of robust operation, i.e., not be susceptible to sodium overcharging and resultant cell failure.